Controlled pressure enclosure

ABSTRACT

The present invention relates to an external cooling system for a molten film tube produced by a blown film tubular extrusion process, comprised of one or more enclosures with one or more respective cavities that directly receive a portion of cooling gas emanating from one or more associated cooling elements. Each enclosure includes a port containing a variable exhaust device and optional flow buffer, acting to maintain a pressure differential between the cavity and an adjacent inside volume of the molten film tube, adjustable to optimize molten film tube stability cooling element efficiency and spaced apart dimension between cooling elements. Significant increases in production speeds are achieved with improved film quality over an increased range of tubular film sizes, down to a minimum size which occurs when operating at zero internal to molten film tube pressure.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a method and apparatus for cooling.The present disclosure relates more particularly to a method andapparatus for high performance cooling.

Description of Related Art

Various methods to manufacture thermoplastic blown films are well knownin the plastics art, and typically involve forming a continuous,vertically oriented, seamless, annular plastic film commonly referred toas the “tube” or “bubble”. Thermoplastic material is melted and pumpedby an extruder through a blown film die (die), exiting as an annularflow of a molten film, continuously drawn upward by a pair of drivensqueeze rollers. Gas is typically manually injected through the die tothe interior of the exiting annular flow of molten film. The drivensqueeze rollers act to prevent gas from escaping, trapping the injectedgas inside, forming a molten film tube which is inflated by the injectedgas until at the desired size and the die is sealed off to preventinflation gas from escaping. The molten film tube is pulled upward bythe driven squeeze rollers, flowing generally upward from the diethrough a cooling system, where it stretches, expands, and cools aroundthe now trapped column of injected gas until it solidifies at a frostline into a solidified film tube. The solidified film tube passesthrough various stabilizers and enters a flattening device, whichconverts the tube into a flattened double thickness thermoplastic sheetof film known as “lay-flat”. The lay-flat passes through the drivensqueeze rollers, and is conveyed to downstream converting equipment suchas winders and bag making machines for further processing.

To remain competitive, manufacturers of blown film must maximizethroughput rate and quality, however cooling system performance is asignificant limiting factor. The weight of thermoplastic that isextruded per unit time divided by the circumference of the die exit,provides a commonly used measure of throughput performance, and isexpressed in units of PPH/Inch, Pounds Per Hour per Inch of die exitcircumference. Many different cooling systems have been developed andemployed, both external and internal to the tube, and to varying degreesthese systems have achieved commercial success.

Blown film cooling systems provide a flow of cooling gas typicallyexternal, but in many cases also internal to the molten film tube.Cooling systems are designed using well known Bernoulli and Coandăprinciples, and in many cases, apply the cooling gas to flow generallyalong the surface of the molten film tube to create holding forces onthe molten film tube, providing for both stability and cooling of themolten film tube. Excessive holding forces, if present, can causevibration, flutter, and high noise levels in the process, and can pullthe molten film tube into undesirable contact with the cooling element,creating drag and causing marks and instability in the molten film tube.In other cases, cooling gas is instead applied generally against thesurface of the molten film tube, typically creating turbulent coolingwith repelling forces, requiring a separate means to stabilize themolten film tube.

External cooling systems, generally provide the primary means forstabilization and cooling of the molten film tube, are generally easy tooperate and used on most blown film extrusion processes. Externalcooling systems provide a flow of cooling gas along the outside surfaceof the molten film tube that typically generates holding forces whilecooling the molten film tube, until the cooling gas dissipates into thesurrounding atmosphere. Less typically, cooling gas is aimed generallyinward generating repelling forces while cooling the molten film tube,undesirably requiring a separate means to hold and stabilize the moltenfilm tube.

Present art external cooling systems are made up of various types ofcooling elements. The earliest cooling element, known as a “Single Flowair ring”, still in common use today, applies a single flow of coolinggas around the molten film tube. Single Flow cooling elements typicallyproduce good film quality, but at lower throughput rates. Additionalflows of cooling gas have been added to cooling elements over time tocreate various multiple flow designs, such as “Dual Flow”, “Triple Flow”or “Quad Flow” designs, and some external cooling systems pair coolingelements into various configurations, depending on the application, toform what is generically known as a “Tandem” air ring. External coolingsystems are typically fixed in place, but can be made adjustable inheight above the die to allow extending the cooled surface area alongthe molten film tube, producing higher throughput, but also resulting ingreater unsupported surface area between the cooling element and die,which is the hottest and weakest portion of the molten film tube, whichcan lead to degraded stability, making it more difficult to operate andpotentially leading to a narrower range of film sizes.

In contrast, internal cooling systems typically do not provide primarystabilization, and are selectively used typically to generate additionalthroughput beyond the capability of an external cooling system. Internalcooling systems replace manual gas injection and inflate the molten filmtube with a flow of an internal supply gas that enters through the die.Although some recent high throughput internal cooling systems applycooling gas to create holding forces, more typically cooling gas isdirected against the inside surface of the molten film tube, acting togenerally repel and cool the inside surface of the molten film tube. Theflow of internal supply gas is trapped inside the bubble and cannotdissipate into the atmosphere, therefore complex control systems areused to balance a flow of internal exhaust gas that exits through thedie to maintain a constant bubble size as is well known and understoodby those skilled in the art. Internal cooling systems can be difficultor even impossible to use depending on such factors as operator skill,thermoplastic material properties, and the physical size and design ofthe associated die.

It is highly desired to overcome the drawbacks of prior artthermoplastic cooling systems and provide a cooling system thatsignificantly increases throughput rate, maximizes aerodynamic holdingforces, allows relatively large unsupported regions of the molten tubewith good stability, produces a wide range of film sizes, prevents dragon the molten film surface, minimizes turbulence, vibration and flutter,does not produce high sound power levels, and is simple and easy tocontrol.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present disclosure toprovide a method and apparatus for cooling.

A first exemplary embodiment of the present disclosure presents anapparatus for cooling. The apparatus includes at least one enclosureincluding a cavity with operational extents further defined by a moltenfilm cavity portion and a cooling element cavity portion. The cavityoperable for receiving at least a portion of cooling gas from at leastone cooling element, wherein the at least one enclosure is operable tomaintain a predetermined pressure differential between an inside surfaceand an outside surface of the molten film cavity portion.

A second exemplary embodiment includes wherein the predeterminedpressure differential maintains a stability of the molten film cavityportion and a cooling efficiency of the at least one cooling element.

A third exemplary embodiment includes wherein the at least one enclosurefurther including at least one port maintaining a variable exhaustdevice operable for moving a portion of cooling gas from the cavitythrough the at least one port to a surrounding atmosphere to maintainthe predetermined pressure differential.

A fourth exemplary embodiment includes wherein the apparatus furtherincludes a flow buffer including a passage into the cavity, the passagefluidly connecting the cavity to the surrounding atmosphere.

A fourth exemplary embodiment of the present disclosure presents amethod for cooling. The method includes receiving, by at least oneenclosure, at least a portion of cooling gas from at least one coolingelement, the at least one enclosure includes a cavity with operationalextents further defined by a molten film cavity portion and a coolingelement cavity portion. The method further includes maintaining, by theat least one enclosure, a predetermined pressure differential between aninside surface and an outside surface of the molten film cavity portion.

The following will describe embodiments of the present invention, but itshould be appreciated that the present invention is not limited to thedescribed embodiments and various modifications of the invention arepossible without departing from the basic principles. The scope of thepresent disclosure is therefore to be determined solely by the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a device suitable for use inpracticing exemplary embodiments of this disclosure.

FIG. 2 is a close-up view of an exemplary flow buffer suitable for usein practicing exemplary embodiments of this disclosure.

FIG. 3 is a close-up cross sectional view of an alternative exemplarycooling element suitable for use in practicing exemplary embodiments ofthis disclosure.

FIG. 4 is a cross sectional view of an alternative device suitable foruse in practicing exemplary embodiments of this disclosure.

FIG. 5 is a cross sectional view of yet another device suitable for usein practicing exemplary embodiments of this disclosure.

FIG. 6 is a cross sectional view of yet another device suitable for usein practicing exemplary embodiments of this disclosure.

FIG. 7 is a logic flow diagram in accordance with a method and apparatusfor performing exemplary embodiments of this disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of the present disclosure relate to a highperformance cooling system for the blown film tubular extrusion processproviding increased throughput rate at high quality. Embodiments of thehigh performance cooling system include one or more enclosures orcontrolled pressure enclosures, creating a gas volume cavity (cavity)around the molten film tube that is isolated from the surroundingatmosphere. The cavity directly receives at least a portion of coolinggas that emanates, generally along the outside surface of the moltenfilm tube, from one or more associated cooling elements. The extents ofthe cavity are formed by the combination of enclosure walls, the portionof the cooling elements in contact with the cavity (also referred to asthe cooling element cavity portion), and the portion of the molten filmtube in contact with the cavity (also referred to as the molten filmcavity portion).

Each enclosure incorporates a variable exhaust device that adjustablytransfers gas through a port in the enclosure, from the associatedcavity to the surrounding atmosphere, allowing for pressure adjustmentrelative to the surrounding atmosphere of the cavity within eachenclosure. A substantially constant internal tube pressure, usually muchless than 1″ H2O (relative to the surrounding atmosphere), is generatedas the molten film tube stretches and forms around the trapped internalgas volume contained within the molten film tube. Resulting cavitypressure acts directly on the outside surface of the molten film cavityportion, and internal tube pressure acts directly on the inside surfaceof the molten film cavity portion, to create a predetermined pressuredifferential across the molten film cavity portion. The predeterminedpressure differential is adjusted to maximize the stability of themolten film cavity portion and the cooling efficiency of the coolingelement cavity portion, to provide higher throughput rate, and betterfilm quality.

The variable exhaust device preferably would be a fan means, chosen withoperating characteristics incapable of creating a predetermined pressuredifferential large enough to stretch the flow of the molten film tubeand thus the molten film cavity portion in between the cooling elementsand hang up on associated cooling elements, causing an interruption inthe flow of the molten film tube. Typical fan designs have well definedand wide range of operating characteristics, published as “fan curves”,easily chosen by those skilled in the art. To simplify adjustment ofpredetermined pressure differential, allow for a broader selection ofvariable exhaust device, and further prevent hang ups, a flow buffer ispreferably added to each enclosure to allow gas to exchange between thecavity and the surrounding atmosphere. The simplest form of a flowbuffer is a passage through the wall of the enclosure fluidly connectingthe cavity to the surrounding atmosphere. As gas flow through thevariable exhaust device is adjusted relative to the cooling gas cavityportion, a flow of gas through the passage occurs. The flow of gasthrough the passage creates an associated passage pressure drop relativeto surrounding atmospheric pressure, which establishes cavity pressureto create the desired predetermined pressure differential. The variableexhaust device and passage are sized to generate the desired range ofpredetermined pressure differential, over the expected range of coolinggas flow, acting together to form a fast acting cavity pressureregulator.

Advantageously, a freely swinging flapper hangs by gravity generallyinside the flow buffer passage. When cavity pressure equals atmosphericpressure, no gas flows through the passage, and the flapper hangsstraight down creating a maximum obstruction in the passage. Aspredetermined pressure differential adjustments are made, gas flowthrough the passage changes, causing a variable deflection of theflapper which variably obstructs the passage in the direction the flowof gas through the passage. The position of the flapper provides an easyto interpret, visual indication of direction and quantity of the flow ofgas through the passage.

Pressure regulating characteristics of the flow buffer can easily be setby giving the flapper a predetermined weight and geometry. The geometryof the passage can also take many forms (i.e. shapes) to achieve verysmooth, fast acting pressure regulation, easily adjusted by the variableexhaust device. Embodiments of the flow buffer include more complexdesigns provided they allow for variable gas exchange with associateddefined pressure drop between the cavity and the surrounding atmosphere.

Embodiments of the disclosure and the divergent cooling elements asdescribed herein can operably be arranged in a four (4) element shortstack configuration topped with a dual flow air ring, as is described inco-pending application titled High Performance Cooling Element filed onJan. 15, 2016, with first named inventor Robert E. Cree, filed underSer. 14/997,157, hereby incorporated by reference. Stable operation ofthe embodiments of this disclosure can be achieved with a spaced apartdimension between cooling elements greater than 4 inches. Further, zerointernal pressure within the molten film tube can be achieved, providingstable straight up (from the final cooling element) tube formation.Additionally, internal tube pressure can be increased yielding the fullrange of larger film sizes normally able to be produced. Throughputrates can be increased in excess of 65% over conventional Dual Flowcooling means.

FIG. 1 shows a cross sectional view of a typical blown film extrusionprocess employing an enclosure 28 of the present invention with a shortstack cooling system. In FIG. 1-FIG. 6, all thin arrows indicating adirection are for illustrative purposes only, labeled for example as AF,and indicate a direction flow of a fluid (e.g. cooling gas). Further,Thick arrows indicating a direction are for illustrative purposes only,labeled for example as MF, and indicate a direction flow of a plasticfilm material (e.g. molten film tube). Thermoplastic resin is introducedthrough feed hopper 2 into extruder 4 where the resin is melted, mixedand pressurized. Molten resin is conveyed through melt pipe 6 into a diemeans 8 that forms it into an annular molten flow that exits generallyfrom the top surface of die means 8 as a molten film tube 12.

Internal gas supply conduit 10 operably provides an internalcooling/inflating gas through die means 8 to the interior of molten filmtube 12 and solidified film tube 16. Internal gas exhaust conduit 9operably removes internal cooling/inflating gas through die means 8 asrequired to maintain a desired trapped tube volume of gas inside moltenfilm tube 12 and solidified film tube 16, further contained by niprollers 20. Gas flow through Internal gas supply conduit 10 and Internalgas exhaust conduit 9 are controlled by methods commonly understood bythose skilled in the art. Molten film tube 12 expands outwardly aroundthe trapped tube volume of gas and is drawn upwardly by nip rollers 20while being cooled to solidify at freeze line 14 forming solidified filmtube 16. Solidified film tube 16 is collapsed by flattening guides 18before passing through nip rollers 20 forming flattened film 22.Flattened film 22 is then conveyed to downstream equipment forconversion into usable products as desired.

Annular cooling elements 23, 24 a-d, and 26 are arranged coaxial withand in the direction of flow of molten film tube 12. Cooling elements23, 24 a-d, and 26, each supplied with cooling gas from a suitableexternal source, direct associated cooling gas alongside molten filmtube 12, generally in the same and/or opposite direction to the flow ofmolten film tube 12, acting to stabilize and cool molten film tube 12.

Upward cooling gas traveling generally in the direction of flow ofmolten film tube 12 from cooling elements 23 and 24 a-c, and downwardcooling gas traveling generally opposite the direction of flow of moltenfilm tube 12 from cooling elements 24 a-d flows directly into a cavity Caround molten film tube 12. Cavity C is contained and isolated from thesurrounding atmosphere by enclosure 28 with additional extents formed bythe portion of the cooling elements 23 and 24 a-d in contact with cavityC (cooling element cavity portion), and the portion of the molten filmtube 12 in contact with cavity C (molten film cavity portion). Coolinggas entering cavity C flows alongside and cools molten film tube 12, andexhausts between cooling elements 23 and 24 a-d, and is collected forfurther processing by enclosure 28. Generally upwardly directed coolinggas from cooling element 26 flows unrestricted, along molten film tube12, directly influenced by the surrounding atmosphere, while cooling andallowing for free expansion of molten film tube 12.

Variable exhaust device 30, installed in a port passing throughenclosure 28, conveys gas from cavity C to the surrounding atmosphere.The choice of variable exhaust device 30 is important. If variableexhaust device 30 is too big or powerful, excessive cavity C pressurescould develop inside enclosure 28 sufficient to cause hang-ups of moltenfilm tube 12. Variable exhaust device 30 is preferably chosen to be of alow pressure, high flow design, sufficient to provide desired pressuresand flows. The pressure of cavity C relative to the surroundingatmosphere is adjusted by variable exhaust device 30 using a variablecontroller means 32, to create a predetermined pressure differentialacross the molten film cavity portion that maximizes the stability ofthe molten film cavity portion and the cooling efficiency of the coolingelement cavity portion, to provide higher throughput rate, and betterfilm quality.

Embodiments of enclosure 28 may include a flow buffer 34, minimallyincluding a passage through the wall of enclosure 28 fluidly connectingcavity C to the surrounding atmosphere. As gas flow through the variableexhaust device 30 is adjusted relative the cooling gas entering cavityC, the flow of gas through flow buffer 34 changes. The flow of gas flowbuffer 34 creates an associated pressure drop relative to surroundingatmospheric pressure, which establishes cavity C pressure and theassociated predetermined pressure differential across the molten filmcavity portion.

Selectively added freely swinging flapper 36 hangs by gravity generallyinside the passage of flow buffer 34. When cavity C pressure equalsatmospheric pressure, no gas flows through flow buffer 34, and theflapper hangs straight down creating a maximum obstruction in thepassage. As predetermined pressure differential adjustments are made,gas flows through flow buffer 34, causing a variable deflection offlapper 36 which variably obstructs flow buffer 34 in the direction theflow of gas through the passage. The position of flapper 36 provides aneasy to interpret, visual indication of direction and quantity of theflow of gas through flow buffer 34. Depending on the choice of variableexhaust device 30, the characteristics of optional flow buffer 34 caneasily be set by predetermining the weight and geometry of flapper 36and the passage geometry of flow buffer 34 to achieve very smooth, fastacting regulation of cavity C pressure, over the desired range ofpredetermined pressure differential across the molten film cavityportion, adjustable by variable controller means 32.

FIG. 2 shows a magnified partial cross sectional view enclosure 28 withoptional flow buffer 34 including flapper 36. Enclosure 28 is providedwith optional flow buffer 34 installed minimally as a passage throughthe wall of enclosure 28 and includes freely swinging flapper 36 thathangs by gravity generally inside the passage of flow buffer 34 andswings freely about pivot 37. Air is allowed to pass in either directionthrough flow buffer 34, between the internal portion of enclosure 28(cavity C) and the surrounding atmosphere, creating an associatedpressure differential across flow buffer 34. As air flows in eitherdirection through flow buffer 34, freely swinging flapper 36 rotatesabout pivot 37 to move under the influence of gravity, in the directionof air flow or to hang straight down under a no flow condition forming aflow dependent variable cross section within flow buffer 34 formedbetween the passage extents and flapper 36. Pressure regulatingcharacteristics of flow buffer 34 can easily be set by adjustingassociated passage geometry and the geometry and weight of freelyswinging flapper 36 to achieve very smooth, fast acting pressureregulation of cavity C, contained inside enclosure 28.

FIG. 3 shows a cross sectional view of a typical blown film extrusionprocess with a short stack cooling system employing multiple enclosures28 of the present invention. Each enclosure 28, is adjusted by anassociated variable controller means 32 acting on an associated variableexhaust device 30, and associated optional flow buffer 34 with furtheroptional freely swinging flapper 36, each enclosure 28 actingindependently on one or more associated cooling element(s) as previouslydescribed. Further, the area between cooling elements 23 and 24 a isshown without an associated enclosure 28, forming an uncontrolled areadirectly influenced by the surrounding atmosphere. Any number ofenclosures 28 and uncontrolled areas can be employed in any order, eachincorporating any number of cooling elements. Additionally, the numberof cooling elements present in the stack is not limited and can be asmany or as few, as is desired, including the full stack cooling systemthoroughly described in prior art.

The short stack cooling system depicted, preferentially includes highperformance, divergent cooling elements described in co-pendingapplication titled High Performance Cooling Element filed on Jan. 15,2016, with first named inventor Robert E. Cree, filed under Ser. No.14/997,157, the contents of which is hereby incorporated by reference.Cooling gas supply conduits 60, spaced generally inside and around theperimeter of cooling elements 23, 24 a, 24 b and 24 c, forming a commonsupply of cooling gas and allowing exhaust gas to flow between adjacentcooling gas supply conduits 60, such as is well known and described inprior art stackable cooling systems. Cooling gas supply conduits 60 alsoact to space apart and locate concentric to molten film tube 12 each ofthe associated cooling elements 23, 24 a, 24 b and 24 c. Cooling element24 d is advantageously shown supplied with cooling gas in common withcooling element 26, forming a high performance triple flow air ring atthe top of the stack. Cooling element 26 is shown as a single flow airring, but can include more than one flow of cooling gas forming amultiple flow air ring, exiting to flow unrestricted, generally upwardand along molten film tube 12, directly influenced by the surroundingatmosphere, while cooling and allowing for free expansion of molten filmtube 12. Cooling element 26 may also be omitted, allowing cooling gasexiting from the upper most located high performance, divergent coolingelement 24 d, with frost line 14 either located above the upper mostdivergent cooling element 24 d and allow for free expansion of moltenfilm tube 12 or within or below the upper most divergent cooling element24 d to constrain the molten film tube 12.

FIG. 4 shows a cross sectional view of a typical blown film extrusionprocess with tandem air ring cooling system employing enclosure 28 ofthe present invention. Cooling element 23 is depicted as, but notlimited to a single flow design, providing cooling gas directly into thelower portion of cavity C associated with enclosure 28. Cooling element26 is depicted as, but not limited to a triple flow design, in thiscase, providing a portion of its cooling gas directly into the upperportion of cavity C of enclosure 28. The cavity C pressure withinenclosure 28 is adjusted by associated variable controller means 32acting on variable exhaust device 30, and optional flow buffer 34 withfreely swinging flapper 36, such that molten film tube 12 is urged intooptimized cooling proximity with associated cooling elements 23, 24 dand 26, resulting in improved throughput rate and film quality.

FIG. 5 shows a cross sectional view of a typical blown film extrusionprocess with a raised up triple flow cooling system, employing enclosure28 of the present invention. The lower portion of enclosure 28 ispreferably sealed as shown to the top of die 8, or optionally can bespaced apart intermediate die 8 and cooling element 26, forming anannular barrier surrounding, but not contacting molten film tube 12.Cooling element 26 is depicted as, but not limited to a triple flowdesign, such that at least a portion of its associated cooling gas isprovided directly into the upper portion of cavity C associated withenclosure 28. The pressure within enclosure 28 is adjusted as previouslydescribed, by associated variable controller means 32 acting on variableexhaust device 30, and optional flow buffer 34 with further optionalfreely swinging flapper 36, such that molten film tube 12 is urged intooptimized cooling proximity with associated cooling elements 24 d and26, resulting in improved throughput rate and film quality.

FIG. 6 shows a cross sectional view of a typical blown film extrusionprocess with tandem air ring cooling system employing enclosure 28 ofthe present invention. Cooling element 23 is depicted as, but notlimited to a single flow design, providing cooling gas directly into thelower portion of cavity C associated with enclosure 28. Cooling element26 is depicted as, but not limited to a dual flow design, preferablyspaced above enclosure 28 disposed in this case, to form an annularbarrier surrounding, but not contacting molten film tube 12, acting toisolate enclosure 28's influence on cooling element 26. Alternatively,cooling element 26 can form the upper extent of enclosure 28 if desired,similar to the cooling system of FIG. 4, but as a dual flow air ringwithout a divergent cooling element (FIG. 4 24 d). The pressure withincavity C associated with enclosure 28 is adjusted as previouslydescribed, by associated variable controller means 32 acting on variableexhaust device 30, and optional flow buffer 34 with further optionalfreely swinging flapper 36, such that molten film tube 12 is urged intooptimized cooling proximity with associated cooling element 23 and to asmaller degree (due to the remoteness), cooling element 26, resulting inimproved throughput rate and film quality.

The present invention is presented on an upward blown film extrusionprocess, but equally applies to horizontal or downward versions of theblown film extrusion process, without limit.

Referring to FIG. 7, presented is a logic flow diagram in accordancewith a method and apparatus for performing exemplary embodiments of thisdisclosure. Block 702 presents receiving, by at least one enclosure, atleast a portion of cooling gas from at least one cooling element, the atleast one enclosure comprising a cavity with operational extents furtherdefined by a molten film cavity portion and a cooling element cavityportion; and maintaining, by the at least one enclosure, a predeterminedpressure differential between an inside surface and an outside surfaceof the molten film cavity portion. Then block 704 presents wherein thepredetermined pressure differential maintains a stability of the moltenfilm cavity portion and a cooling efficiency of the at least one coolingelement.

Some of the non-limiting implementations detailed above are alsosummarized at FIG. 7 following block 704. Block 706 relates to whereinthe at least one enclosure comprises at least one port maintaining avariable exhaust device operable for moving a portion of cooling gasfrom the cavity through the at least one port to a surroundingatmosphere to maintain the predetermined pressure differential. Thenblock 708 states wherein the variable exhaust device is inoperable forexceeding the predetermined pressure differential causing a hang up ofthe flow of the molten film tube. Block 710 then further specifies theat least one enclosure further comprising at least one flow buffercomprising a passage into the cavity, the passage fluidly connecting thecavity to the surrounding atmosphere allowing a flow of gas into and outof the cavity.

Following block 710, block 712 relates to wherein the at least one flowbuffer comprises a flapper operable to (i) variably obstruct a flow ofgas through the passage and (ii) indicate a direction and quantity ofthe flow of gas through the passage. Block 714 then states wherein theflapper has a predetermined weight and geometry. Block 716 thenspecifies wherein the cooling element cavity portion comprises aplurality of cooling elements each one of the plurality of coolingelements providing at least a portion of cooling gas received by thecavity.

Block 718 then relates to wherein the at least one cooling element is asingle flow air ring or a dual flow air ring. Block 720 states whereinthe at least one cooling element is a triple flow air ring. Then block722 specifies wherein the at least one cooling element is a divergentcooling element having a divergent cooling interface operable forexpelling the cooling gas. Finally block 724 indicates wherein the atleast one enclosure comprises a plurality of enclosures, each one of theplurality of enclosures operable for receiving at least an associatedportion of cooling gas to maintain an associated predetermined pressuredifferential.

The logic flow diagram may be considered to illustrate the operation ofa method. The logic flow diagram may also be considered a specificmanner in which components of a device are configured to cause thatdevice to operate, whether such a device is a blown film tubularextrusion device, controlled pressure enclosure, or divergent coolingelement, or one or more components thereof.

Embodiments of the present invention has been described in detail withparticular reference to particular embodiments, but it will beunderstood that variations and modifications can be effected within thespirit and scope of the invention. The presently disclosed embodimentsare therefore considered in all respects to be illustrative and notrestrictive. The scope of the invention is indicated by the appendedclaims, and all changes that come within the meaning and range ofequivalents thereof are intended to be embraced therein.

The invention claimed is:
 1. An apparatus for cooling, the apparatuscomprising: at least one enclosure comprising a cavity with operationalextents further defined by a molten film cavity portion and a coolingelement cavity portion, the cavity operable for receiving at least aportion of cooling gas from at least one cooling element, wherein the atleast one enclosure is operable to maintain a predetermined pressuredifferential between an inside surface and an outside surface of themolten film cavity portion, the at least one enclosure comprising atleast one flow buffer comprising a passage into the cavity, the passagefluidly connecting the cavity to the surrounding atmosphere allowing aflow of gas into and out of the cavity.
 2. The apparatus according toclaim 1, wherein the predetermined pressure differential maintains astability of the molten film cavity portion and a cooling efficiency ofthe at least one cooling element.
 3. The apparatus according to claim 2,the at least one enclosure further comprising at least one portmaintaining a variable exhaust device operable for moving a portion ofcooling gas from the cavity through the at least one port to asurrounding atmosphere to maintain the predetermined pressuredifferential.
 4. The apparatus according to claim 3, wherein thevariable exhaust device is inoperable for exceeding the predeterminedpressure differential causing a hang up of a flow of a molten film tube.5. The apparatus according to claim 1, wherein the at least one flowbuffer comprises a flapper operable to (i) variably obstruct a flow ofgas through the passage and (ii) indicate a direction and quantity ofthe flow of gas through the passage.
 6. The apparatus according to claim5, wherein the flapper has a predetermined weight and geometry.
 7. Theapparatus according to claim 1, wherein the cooling element cavityportion comprises a plurality of cooling elements, each one of theplurality of cooling elements providing at least a portion of thecooling gas received by the cavity.
 8. The apparatus according to claim1, wherein the at least one cooling element is a single flow air ring ora dual flow air ring.
 9. The apparatus according to claim 1, wherein theat least one cooling element is a triple flow air ring.
 10. Theapparatus according to claim 1, wherein the at least one cooling elementis a divergent cooling element having a divergent cooling interfaceoperable for expelling the cooling gas.
 11. The apparatus according toclaim 1, wherein the at least one enclosure comprises a plurality ofenclosures, each one of the plurality of enclosures operable forreceiving at least an associated portion of cooling gas to maintain anassociated predetermined pressure differential.
 12. A method forcooling, the method comprising: (a) receiving, by at least oneenclosure, at least a portion of cooling gas from at least one coolingelement, the at least one enclosure comprising a cavity with operationalextents further defined by a molten film cavity portion and a coolingelement cavity portion; and (b) maintaining, by the at least oneenclosure, a predetermined pressure differential between an insidesurface and an outside surface of the molten film cavity portion, the atleast one enclosure further comprising at least one flow buffercomprising a passage into the cavity, the passage fluidly connecting thecavity to the surrounding atmosphere allowing a flow of gas into and outof the cavity.
 13. The method according to claim 12, wherein thepredetermined pressure differential maintains a stability of the moltenfilm cavity portion and a cooling efficiency of the at least one coolingelement.
 14. The method according to claim 12, wherein the at least oneenclosure comprises at least one port maintaining a variable exhaustdevice operable for moving a portion of cooling gas from the cavitythrough the at least one port to a surrounding atmosphere to maintainthe predetermined pressure differential.
 15. The method according toclaim 14, wherein the variable exhaust device is inoperable forexceeding the predetermined pressure differential causing a hang up of aflow of a molten film tube.
 16. The method according to claim 14,wherein the at least one flow buffer comprises a flapper operable to (i)variably obstruct a flow of gas through the passage and (ii) indicate adirection and quantity of the flow of gas through the passage.
 17. Themethod according to claim 16, wherein the flapper has a predeterminedweight and geometry.
 18. The method according to claim 12, wherein thecooling element cavity portion comprises a plurality of cooling elementseach one of the plurality of cooling elements providing at least aportion of cooling gas received by the cavity.
 19. The method accordingto claim 12, wherein the at least one cooling element is a single flowair ring or a dual flow air ring.
 20. The method according to claim 12,wherein the at least one cooling element is a triple flow air ring. 21.The method according to claim 12, wherein the at least one coolingelement is a divergent cooling element having a divergent coolinginterface operable for expelling the cooling gas.
 22. The methodaccording to claim 12, wherein the at least one enclosure comprises aplurality of enclosures, each one of the plurality of enclosuresoperable for receiving at least an associated portion of cooling gas tomaintain an associated predetermined pressure differential.